According to The Associated Press, he attended medical school for a few years but withdrew and didn't graduate. Also, Hamman had no medical residency or the 15 years of clinical experience he claimed.
His colleagues were stunned.
He never treated patients, but he just lectured and taught.
Hamman is telling the truth about being a pilot. He is a captain with United Airlines, but the airline has grounded him after learning about the deception in August.
Hammam's attorney said he looks forward to clearing up the issue.
The Associated Press contributed to this report.